The present invention relates to focusing structure in an information reading apparatus that reads information on an object of interest (e.g., baggage or mail) and that is to typically be used with a sorting system which is capable of automatic sorting of the object of interest as it is conveyed on a conveyor.
Automatic sorting systems have been known which are capable of automatically sorting baggage, mail, etc., according to the address or point of destination as they are carried on a moving conveyor, etc. Using such an automatic sorting system, the address, point of destination or other information that is indicated on the surface of the object of interest is read using a reading apparatus disposed in the vicinity of the conveyor. The object on the conveyor is carried in one direction or another and collected there depending upon the information read. The object is thereby sorted in accordance with the address or point of its destination. The reading apparatus comprises a camera section that is composed of an optical system (lens), a sensor and an electric circuit, and an information processing section composed of a microcomputer. In the camera section, the image of the information indicating area formed on the focusing surface of the sensor by the lens is converted to an electric signal with the sensor, and the electric signal is supplied to the information processing section, which will then read the necessary information by pattern recognition or some other method in response to a signal from the camera section.
If the size of the object being conveyed is not uniform and the camera section is held at a fixed position, the distance from the information indicating area of the object to the camera section will vary and the image of that area will not properly be focused on the sensor to enable accurate reading of the necessary information. To avoid this problem, the camera section is adapted to be either automatically or manually movable so that the distance from the information indicating area of the object to the camera as measured with an instrument or the eye, respectively, is held constant.
The prior art reading apparatus however, has had the following problems. First, the camera section is composed of a highly precise optical system (lens), sensor and electric circuit and if the size of the object being conveyed is so uneven as to cause frequent change in the distance to the information indicating surface, the camera section must accordingly be moved frequently. As a result, troubles will often occur on account of vibrations or impacts caused by frequent moving and stopping of the camera, and this will markedly reduce the durability of the camera section. Secondly, there is a need to maximize the conveyor speed in order to improve the efficiency of sorting operations, but because of the low durability of the camera section and its high inertia due to its comparatively large mass, the camera section cannot by moved at a speed beyond a certain limit and the resulting limitation on the conveyor speed precludes improvement in the operational efficiency.